This study aimed to evaluate the efficiency of Photo-Fenton and Fenton processes in reducing organic matter of dairy effluent. An Orthogonal Array L9 Taguchi was used to determine optimal conditions of acidity media, temperature, Fenton concentration and UV radiation intensity. Reaction time was set up to 60 min. Optimized parameters were: pH 3.0, temperature, Fenton reagent concentration and UV radiation at the highest level. The Dissolved Organic Carbon percentage reduction (DOC) was 91%. An effective degradation study was carried out, in which, the reduction percentage was found to be less than the most efficient DOC removal. A cost/benefit evaluation of the AOP process employed on the in natura dairy effluent treatment showed that the reagent consumption the main cost of the process. The highest efficiency experiment for the dairy effluent of this study had operational costs lower than US $0.50 to Photo-